1. Field of the Invention
This invention relates to new and useful improvements bearing assemblies for use on downhole motors and to motor-bearing assemblies.
2. Brief Description of the Prior Art
Drilling apparatus wherein a drill bit is operated by a downhole motor, such as positive displacement fluid motors or a turbine driven motors, are well known in the prior art. In such motors, the drill bit is rotated by a rotor being turned by flow of fluid, such as drilling fluid through the motor assembly.
In such downhole motor assemblies, bearings are provided which are sometimes part of the overall motor assembly and which are sometimes provided in a separate bearing pack or bearing assembly which is fastened or secured to the motor housing. The bearings support the drilling thrust on the shaft during the drilling operation. Other bearings transfer hydraulic thrust from the motor to the shaft when the motor is pulled from the bore hole or when the drill bit is lifted off bottom.
When a downhole motor is operating, there are two downward forces acting on the rotor shaft, viz., hydraulic downthrust and rotor weight, and one upward thrust, viz., bit weight (the reactive upward thrust resulting from the action of the drill against the earth formation). In normal drilling operations, it is often possible to adjust the bit weight so that it nearly balances the downward forces and thus unloads the bearings. This greatly extends the life of the conventional motor bearings. This is often done with large diameter turbodrills, e.g., 5-12 in. diameter, where the downward thrusts range from 10,000-30,000 pounds (150-1000 psi) and the rubber thrust bearings used in these turbodrills fail rapidly if nearly balanced bit weights are not used.
When downhole motors are designed for high pressure, high speed operation, e.g. 10,000 psi, the bearing life is less than 1.0 hour as compared to 200 hours at conventional low pressure operation. This rapid wearing out of bearings makes the development of high pressure, high speed downhole motor driven drills almost impossible. It is apparent that high pressure, high speed motors require the development of either higher capacity bearings or means for reducing the bearing load at high bit pressures.
The following patents illustrate some of the types of bearings which have been or are being used in downhole motors, none of which address the problem of high pressure operation:
Tschirky U.S. Pat. No. 3,879,094 discloses a downhole motor consisting of a positive displacement motor having a bearing assembly on the motor housing which has tungsten carbide radial bearings and a plurality of longitudinally spaced axial thrust bearings.
Tiraspolsky U.S. Pat. No. 3,449,030 discloses a bearing assembly for use in downhole motors which includes a plurality of spaced axial thrust bearings having woven wire annular pads which function to absorb shock.
Garrison U.S. Pat. No. 3,594,106 discloses a downhole motor assembly having a plurality of longitudinally spaced axial thrust bearings and a spring mechanism for absorbing shock.
Stodt U.S. Pat. No. 4,135,772 discloses a bearing assembly for a downhole motor driven drill having axially spaced ball bearings for carrying axial thrust loads and having springs interposed between the bearings for absorbing shock.
Crase U.S. Pat. No. 4,260,202 discloses a bearing assembly for downhole motors which includes spaced ball bearing assemblies which include springs for absorbing axial shock.
Winkelmann U.S. Pat. No. 4,388,973 discloses a bearing assembly for a downhole motor in which bearings are spaced by shoulders on a series of sleeves which form a continuous supporting tube on the inside and outside of the bearing structure and supported on the rotating motor shaft. These bearings include springs for absorbing axial shock loads but are not constructed for interchangeability of the positioning of the bearings for determining the amount of upward and downward thrust supported by the bearing assembly.
Maurer et al U.S. Pat. No. 4,114,704 discloses a turbo-drill having means to use the pressure of drilling mud to reverse the application of bearing forces from the lower to the upper thrust bearings, but does not suggest any means for continuously unloading the lower thrust bearings continuously during motor operation.